1. Field of the Invention
Refrigerated display cases of the open well type generally are used for low temperature applications. Access to produce displayed in the case is provided by an opening in the top wall of the case. Typically, air flow across the access opening of the case is from rear to front, with the coldest temperatures in the case being at the rear of the well. Thus the coldest product on display is furthest from the customer.
Because of the location of the access opening, a serious problem in cases of the top display type is the effect radiant heat has on the product. Radiant heat generally travels in straight lines and emanates from either the ceiling or from lights placed directly above the case. Tests have shown that radiant energy can cause the product displayed in a case having a top access opening to be 10.degree. to 20.degree. Fahrenheit (F.) higher than the air temperature traveling over the product.
To negate the effects of radiant heat requires a flow of air perpendicular to the radiant effect to carry radiant heat away from the product faster than it can be input. Thus it is necessary to increase the velocity of the flow of refrigerated air across the access opening to dissipate radiant heat. However, with a single air curtain, an increase in the air velocity of the refrigerated air results in an excessive amount of aspiration with ambient air. Using a double air band in which the inner band is refrigerated and the outer band is unrefrigerated permits increasing the velocity of air flow across the products. The outer air band preserves the integrity of the inner refrigerated air band flowing across the access opening. The use of two air bands, including an outer unrefrigerated air band, permits the use of a high velocity air flow for the two air bands which operates effectively to dissipate the effect of radiant energy and thus maintain the integrity of the product.
2. Prior Art
It should be recognized that the use of multiple air curtains in refrigerated display cases is well known in the art. The broad general concept of having a plurality of streams of air flowing across the display case with the outermost layer or layers of air being an unrefrigerated type is illustrated in the following U.S. Pat. Nos.: Re. 25,735 -- Lamb, 3,063,252 -- Lamb, 3,082,612 -- Beckwith, 3,094,851 -- Beckwith, 3,130,559 -- Beckwith, 3,528,258 -- Brennan. However, it should be noted that in all of the above patents, the display cases were of the upright type in which the problem posed by radiant energy is minimal. Further, the streams of air flowing into such upright display cases was from the top to the bottom of the case to thus form a substantially vertical air curtain.
Of particular interest is the following U.S. Pat. No.: 3,324,676 -- Gerweck. In the above U.S. patent the patent drawing suggests a possible horizontal orientation of a portion of the air curtains but it is not clear that the air flow would be as displayed in FIG. 1 of the drawing because the flow of air would not be constrained to follow the contour of the side wall of the case but rather would flow from outlets 54 and 56 across the access opening provided in the case to inlet 42 and along a substantially vertical path. Although Gerweck discloses two air curtains, the outer one being ambient air and the inner one being refrigerated air, the reference illustrates an upright display case in which the problem of radiant energy is minimal and there is no suggestion that the use of a horizontal air curtain in the subject case is desired or intended. Further, it is not clear that the patent is operative to produce a horizontal air curtain in that it would appear very difficult to change the outer air curtain from a vertical to a horizontal curtain where the refrigerated air from the chamber 24 impinges on the vertically flowing ambient air.